1. Technical Field
The present invention relates to a permanent magnet type motor having a permanent magnet disposed on a rotor, and a method for manufacturing the permanent magnet type motor.
2. Description of the Related Arts
In a permanent magnet type motor, an operating environment temperature and a generated torque are limited by a demagnetization proof stress of a permanent magnet. For example, in rare-earth magnets such as a neodymium magnet, “high-temperature demagnetization” occurs wherein as the operating temperature rises, the demagnetization proof stress drops. Thus, the rare-earth magnets need to be managed in terms of an upper limit of the operating environment temperature and an upper limit of the generated torque under a high-temperature environment.
In order to improve demagnetization proof stress of a permanent magnet type motor, there are a shape-wise improvement of the permanent magnet such as an increase in the thickness of the permanent magnet, and a plan to improve a rotor structure. Furthermore, the demagnetization proof stress of a permanent magnet type motor can also be improved by an improvement in a material of the permanent magnet, such as use of a permanent magnet having a high intrinsic coercive force.
As a technique concerning an improvement in the magnet shape of the permanent magnet, a technique that physically forms a notch in a corner portion of the permanent magnet to intend a drop of a cogging torque and an improvement in the magnetic flux density distribution has been disclosed (for example, see Japanese Patent Application Laid-Open Publication No. 05-176509).